6,054 research outputs found
Generation of spin currents and spin densities in systems with reduced symmetry
We show that the spin-current response of a semiconductor crystal to an
external electric field is considerably more complex than previously assumed.
While in systems of high symmetry only the spin-Hall components are allowed, in
systems of lower symmetry other non-spin-Hall components may be present. We
argue that, when spin-orbit interactions are present only in the band
structure, the distinction between intrinsic and extrinsic contributions to the
spin current is not useful. We show that the generation of spin currents and
that of spin densities in an electric field are closely related, and that our
general theory provides a systematic way to distinguish between them in
experiment. We discuss also the meaning of vertex corrections in systems with
spin-orbit interactions.Comment: 4 page
Extrinsic Entwined with Intrinsic Spin Hall Effect in Disordered Mesoscopic Bars
We show that pure spin Hall current, flowing out of a four-terminal
phase-coherent two-dimensional electron gas (2DEG) within inversion asymmetric
semiconductor heterostructure, contains contributions from both the extrinsic
mechanisms (spin-orbit dependent scattering off impurities) and the intrinsic
ones (due to the Rashba coupling). While the extrinsic contribution vanishes in
the weakly and strongly disordered limits, and the intrinsic one dominates in
the quasiballistic limit, in the crossover transport regime the spin Hall
conductance, exhibiting sample-to-sample large fluctuations and sign change, is
not simply reducible to either of the two mechanisms, which can be relevant for
interpretation of experiments on dirty 2DEGs [V. Sih et al., Nature Phys. 1, 31
(2005)].Comment: 5 pages, 3 color EPS figure
Spin precession and alternating spin polarization in spin-3/2 hole systems
The spin density matrix for spin-3/2 hole systems can be decomposed into a
sequence of multipoles which has important higher-order contributions beyond
the ones known for electron systems [R. Winkler, Phys. Rev. B \textbf{70},
125301 (2004)]. We show here that the hole spin polarization and the
higher-order multipoles can precess due to the spin-orbit coupling in the
valence band, yet in the absence of external or effective magnetic fields. Hole
spin precession is important in the context of spin relaxation and offers the
possibility of new device applications. We discuss this precession in the
context of recent experiments and suggest a related experimental setup in which
hole spin precession gives rise to an alternating spin polarization.Comment: 4 pages, 2 figures, to appear in Physical Review Letter
Spin interference in silicon three-terminal one-dimensional rings
We present the first findings of the spin transistor effect in the Rashba
gate-controlled ring embedded in the p-type self-assembled silicon quantum well
that is prepared on the n-type Si (100) surface. The coherence and phase
sensitivity of the spin-dependent transport of holes are studied by varying the
value of the external magnetic field and the bias voltage that are applied
perpendicularly to the plane of the double-slit ring. Firstly, the amplitude
and phase sensitivity of the 0.7(2e^2/h) feature of the hole quantum
conductance staircase revealed by the quantum point contact inserted in the one
of the arms of the double-slit ring are found to result from the interplay of
the spontaneous spin polarization and the Rashba spin-orbit interaction.
Secondly, the quantum scatterers connected to two one-dimensional leads and the
quantum point contact inserted are shown to define the amplitude and the phase
of the Aharonov-Bohm and the Aharonov-Casher conductance oscillations.Comment: 8 pages, 5 figure
On the nature of steady states of spin distributions in the presence of spin-orbit interactions
In the presence of spin-orbit interactions, the steady state established for
spin distributions in an electric field is qualitatively different from the
steady state for charge distributions. This is primarily because the steady
state established for spin distributions involves spin precession due to
spin-orbit coupling. We demonstrate in this work that the spin density matrix
in an external electric field acquires two corrections with different
dependencies on the characteristic momentum scattering time. One part is
associated with conserved spins, diverges in the clean limit and is responsible
for the establishment of a steady-state spin density in electric fields.
Another part is associated with precessing spins, is finite in the clean limit
and is responsible for the establishment of spin currents in electric fields.
Scattering between these distributions has important consequences for spin
dynamics and spin-related effects in general, and explains some recent puzzling
observations, which are captured by our unified theory.Comment: 10 pages, 1 figur
Anomalous spin-resolved point-contact transmission of holes due to cubic Rashba spin-orbit coupling
Evidence is presented for the finite wave vector crossing of the two lowest
one-dimensional spin-split subbands in quantum point contacts fabricated from
two-dimensional hole gases with strong spin-orbit interaction. This phenomenon
offers an elegant explanation for the anomalous sign of the spin polarization
filtered by a point contact, as observed in magnetic focusing experiments.
Anticrossing is introduced by a magnetic field parallel to the channel or an
asymmetric potential transverse to it. Controlling the magnitude of the
spin-splitting affords a novel mechanism for inverting the sign of the spin
polarization.Comment: 4 pages, 3 figure
Edge Dynamics in a Quantum Spin Hall State: Effects from Rashba Spin-Orbit Interaction
We analyze the dynamics of the helical edge modes of a quantum spin Hall
state in the presence of a spatially non-uniform Rashba spin-orbit (SO)
interaction. A randomly fluctuating Rashba SO coupling is found to open a
scattering channel which causes localization of the edge modes for a weakly
screened electron-electron (e-e) interaction. A periodic modulation of the SO
coupling, with a wave number commensurate with the Fermi momentum, makes the
edge insulating already at intermediate strengths of the e-e interaction. We
discuss implications for experiments on edge state transport in a HgTe quantum
well.Comment: 4 pages, 2 figures; published versio
Hartree-Fock ground state of the two-dimensional electron gas with Rashba spin-orbit interaction
We search for the uniform Hartree-Fock ground state of the two-dimensional
electron gas formed in semiconductor heterostructures including the Rashba
spin-orbit interaction. We identify two competing quantum phases: a
ferromagnetic one with partial spin polarization in the perpendicular direction
and a paramagnetic one with in-plane spin. We present a phase diagram in terms
of the relative strengths of the Rashba to the Coulomb interaction and the
electron density. We compare our theoretical description with existing
experimental results obtained in GaAs-AlGaAs heterostructures.Comment: 5 pages, 2 figure
Interplay of Coulomb interaction and spin-orbit effects in multi-level quantum dots
We study electron transport through a multi-level quantum dot with Rashba
spin-orbit interaction in the presence of local Coulomb repulsion. Motivated by
recent experiments, we compute the level splitting induced by the spin-orbit
interaction at finite Zeeman fields , which provides a measure of the
renormalized spin-orbit energy. This level splitting is responsible for the
suppression of the Kondo ridges at finite characteristic for the
multi-level structure. In addition, the dependence of renormalized -factors
on the relative orientation of the applied field and the spin-orbit
direction following two different protocols used in experiments is
investigated.Comment: 11 pages, 13 figure
Invariant expansion for the trigonal band structure of graphene
We present a symmetry analysis of the trigonal band structure in graphene,
elucidating the transformational properties of the underlying basis functions
and the crucial role of time-reversal invariance. Group theory is used to
derive an invariant expansion of the Hamiltonian for electron states near the K
points of the graphene Brillouin zone. Besides yielding the characteristic
k-linear dispersion and higher-order corrections to it, this approach enables
the systematic incorporation of all terms arising from external electric and
magnetic fields, strain, and spin-orbit coupling up to any desired order.
Several new contributions are found, in addition to reproducing results
obtained previously within tight-binding calculations. Physical ramifications
of these new terms are discussed.Comment: 10 pages, 1 figure; expanded version with more details and additional
result
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